Central nervous system information processing will be studied in the visual and infrared sensory systems of crotalid snakes. The objectives are: 1) to describe quantitatively the processes by which sharpening of spatial resolution (reduction of receptive field center size) is accomplished by midbrain (tectal) infrared sensitive neurons; 2) to construct spatial maps of the tectal surface for the infrared and visual systems in order to determine whether infrared system tectal input and visual tectal input caused by the same physical stimulus are mapped to the same spot in the tectum; 3) to identify multimodal tectal units which receive input from both visual and infrared systems; and 4) to describe quantitatively the dynamical and spatial aspects of each type of input, and of the interaction of inputs in the two modalities. Infrared units in the trigeminal nerve and in the lateral nucleus of the trigeminal are being similarly characterized. Stimuli to be used in these studies will be controlled by the same computer which collects and analyzes single unit response data. Post stimulus response histograms, frequency response curves and measures of linearity will be used to describe the input-output properties of tectal units for the two modalities singly and in combination.